N. Blüthgen, F. Menzel, N. Blüthgen, Measuring specialization in species interaction networks. BMC Ecol. 6, 9 (2006). doi:10.1186/1472-6785-6-9pmid:16907983
Previously, the majority of network analysis was qualitative. Blüthgen et al introduce two quantitative measurements that uses the frequency of interactions to describe specialization at the species level and across a network.